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300tdi Head gasket change


Mark Adams

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  • 1 year later...

Hi Mark, I've got some bad news for you as according to the official Land Rover service manual the 300TDi head must not be skimmed. They state that if the head is warped by more than 0.08 of a millimetre (3.14 thou) it must be discarded!

I have replaced the gasket on a 300TDi whose head presumably has been skimmed and the surprising thing was that when the head was lifted the pistons of cylinders 1 and 4 both had dents caused by being hit by the exhaust valves. Presumably if one is going to skim the head one must also re-cut the valve seats to sink the valves lower.

Often aluminium castings are vacuum impregnated with resin as otherwise they can be porous. Possibly these heads are resin-sealed and machining removes the resin-sealed surface. The Land Rover specialists near where I live used to say that with the 300TDi a lot of people would replace the head gasket but unless the radiator is as-new or uprated, the gasket will soon blow again.

The 300TDi in the Defender is less trouble than the one in the Discovery as the header tank is higher. Good luck.

The good news is that the 300TDi engine is still being made overseas and a brand new head (bare) is not as expensive as might be expected. IMHO however the high mounted water pump on these engines and the cross-flow radiator are a recipe for disaster.

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According to LR there are lots of things you mustn't do, all of which are done regularly. 300Tdi heads are often skimmed, liners are fitted etc etc. It is quite common to see pistons with valve markings on them even if the stand-down and head gasket are correct, often in engines that have never been stripped. If you skim the head a lot it is possible for the glow plugs to contact the centre of the piston but this doesn't seem to do any damage either.

What does cause head gaskets to blow is often incompetence in torqueing and angle-tightening the bolts. There are a few tricks involved that I won't go into here.

The cross-flow radiator can be fixed by drilling a hole in the plate between the top and bottom of the rad. Possibly another design fault. If you get the radiator re-cored get them to drill holes to let the coolant through.

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It may also be worth checking the water pump for free play or if the impellor has sheared off.

And would also check the thermostat is working as it should.

It would not be uncommon for it to run fine after you have done the headgasket under normal driving but may have just pushed it over the edge and made it run hotter when towing.

Lastly worth while checking to see if the viscous fan is locking in when its hot too.

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and NEVER run a Tdi without a thermostat fitted because then the coolant never goes to the radiator at all ..... It is difficult to check if the vicious fan is working properly. If there is any oil on the front face then change it.

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sorry to hi-jack the thread slightly but its relevant (ish). I need to do my head gasket thanks ot crumby plastic filler breaking, is it best to replace the head bolts with new stretch bolts? Also if not required is the tightening sequewnce the same?

thanks

Matt

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sorry to hi-jack the thread slightly but its relevant (ish). I need to do my head gasket thanks ot crumby plastic filler breaking, is it best to replace the head bolts with new stretch bolts? Also if not required is the tightening sequewnce the same?

thanks

Matt

300tdi bolts are NOT and I repeat NOT stretch bolts. They can be used up to 5 times. TD5 bolts ARE stretch bolts and you can feel them stretching as the last degrees of tightening are done. They must not be re-used. If you want to know the difference read up on plastic limits of steels.

The tightening sequence is always the same and must be adhered to. Preferably buy an angle gauge. The other trick is to mark the bolts with chalk. Then if you get called away or something you know where you got to and can carry on from where you left off.

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I decided that I would obtain another cylinder head as I do not trust the one I had so I ordered a second hand head and had it skimmed and tested just got it back so I decided to check the Valve head stand down (as adviced last time). The thicker feeler gauge I can get in all the valves is .6mm some will take slighly thicker but most are just .6 Does anyone know what it should be?

Is this something the engineering works should check when they skim the head?

Mark.

Absolutely they should check it after skimming. For this reason the valves should go with the head when this is done. If the stand down is too little the valve seats should be recut until the stand down is correct. You can't do this yourself. Some engineering places are mines of ignorance about the engines they work on.

Here's a piccy. Note the centre of the piston where the glow plug hit.

P1010004Small-1.jpg

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